Metallic yarn structure



April 23, 1968 J. A. ROBERTS ET Al. 3,378,999

METALLI G YARN STRUCTURE Filed June 17. 1965 3 Sheets-Sheet 1 54 3;;F11. [3/ Q //g Lye/flora.-

April 23, 1968 J. A. ROBERTS ET 1.

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United States Patent 3,378,999 METALLIC YARN STRUCTURE John A. Roberts,North Chelmsford, and Joseph R. Quirk, Woburn, Mass., assignors toBrunswick Corporation, a corporation of Delaware Filed June 17, 1965,Ser. No. 464,721 9 Claims. (Cl. 7139 ABSTRACT OF THE DISCLOSURE A metalyarn structure wherein the filaments are set under pressure while in asubstantially nonelastic state to be free of residual torsion whilehaving a preselected helical twist. The setting of the filaments in thehelical configuration is effected by twisting the filaments in a matrixwhile concurrently effecting constriction thereof to fluidize thefilaments and permit the setting thereof upon release of theconstriction forces in the torsion-free helical configuration.

Specification This invention relates to twisted yarns, e.g. twistedbundles of filaments, and more particularly to yarns and methods offorming yarns of very small diameter filaments in twisted form.

There are many known or anticipated uses for high tensile strength,highly flexible yarns. Such yarns may be formed of synthetic plasticfilaments or metal'filaments adapted to be woven into suitable textilematerials such as sheets or strips, or be embedded or otherwise disposedin other materials such as for reinforcement thereof, providinganti-static characteristics, etc.

In one known method of forming yarns of filaments, a plurality offilaments are disposed in parallel spaced relationship with matrixmaterial extending between the respective filaments. The bundle offilaments is radially constricted such as by drawing of the bundlethrough a drawing die whereby the individual filaments are reduced indiameter. Alternately the bundle may be radially constricted by otherconstricting methods such as by hot or cold rolling. A plurality ofconstricting steps may be employed so as to reduce the filaments to anultimate, extremely small diameter.

The final constricted bundle is then suitably treated to remove thematrix material from the small diameter filaments thereby providing ayarn comprised of a plurality of fine filaments. To provide desirableyarn characteristics it is common to provide in such yarns a twist of anumber of turns per inch. One conventional method of applying such atwist to the filaments is to feed each of the filaments individually toa twisting apparatus which wraps th fiiaments about each other in agenerally helical fashion. This method of providing a twist in thefilaments of the yarns has the serious defect of leaving in thefilaments a resultant torsion tending to untwist the filaments as aresult of the natural resiliency of the filamentary material. Thus theresultant twisted yarn has a tendency to spring or curl to varyingdegrees depending on the amount of twisting and the specific materialsof which the filaments are formed. One attempted solution to thisproblem has been to wrap a plurality of the twisted yarns in reversedirection so that the twist of one yarn offsets the twist of the nextyarn thereby providing a thread wherein the curling tendencies of therespective yarn are counterbalanced. Such a solution however has notproven completely satisfactory as the residual torsion forces cannot befully accurately balanced.

The present invention comprehends an improved yarn structure and methodof forming the same which eliminates the above discussed disadvantagesof the known twisted yarns in an extremely simple and novel manner. Itis, therefore, a principal feature of the present invention to provide anew and improved yarn and method. of forming the same.

Another feature of the invention is the provision of a yarn structurecomprising: a plurality of filaments set free of residual torsion insubstantially coaxial, spaced helical relationship and having engagementtherebetween.

A further feature of the invention is the provision of such a yarnstructure wherein the number of turns per inch of the helical filamentsis preselected to provide a yarn strength substantially equal to thezero gauge length strength of said filaments.

Still another feature of the invention is the provision of such a yarnstructure wherein the total area of the filaments transverse to the axisof the yarn being substantially constant along the axis.

A further feature of the invention is the provision of such a yarnstructure wherein the filaments are disposed in radially spaced,generally cylindrical groups.

Yet another feature of the invention is th provision of such a yarnstructure wherein the plurality of filaments includes axially,substantially rectilinear filament having a diameter larger than thehelical filaments.

A yet further feature of the invention is the provision of such a yarnstructure wherein the plurality of filaments includes filaments spacedat different distances radially of the axis of the set plurality, thediameter of the filaments being inversely related to the spacing thereoffrom the axis.

A further feature of the invention is the provision of such a yarnstructure wherein the number of turns per inch of the filaments in thehelical relationship is greater than 2.

Another feature of the invention is the provision of such a yarnstructure wherein each of the filaments has an outer surface portiondefining a diffusion zone.

Another feature of the invention is the provision of such a yarnstructure comprising a plurality of filaments disposed in generallycoaxial, helical configurations wherein the helical configurations arepermanently set in the filaments by delivering the filaments to aconstricting means while in a bundled arrangement, the constrictingmeans being suitably arranged to constrict the bundled arrangementsufiiciently to cause a hydrostatic plasticizing of the filamentstherein while the bundled filaments are concurrently twisted to causethe filaments to be repositioned within the constricting means incoaxial, spaced helical relationship with each other, and withdrawingthe helically arranged filaments from the constricting means to releasethe hydrostatic pressure whereby the filaments set in the helicalconfiguration free of residual torsion.

A further feature of the invention is the provision of a method ofmaking a twisted yarn comprising the steps of providing a plurality ofparallel, spaced filament with matrix material therebetween, effecting aplasticizing of the filaments in the bundle, providing a twist in theplasticized filaments in the bundle, discontinuing the plasticizing ofthe filaments to cause the filaments to set in a substantially coaxial,spaced helical configuration free of residual torsion, and removing thematrix material.

Another feature of the invention is the provision of such a methodwherein the plasticizing step comprises a step of radially constrictingthe bundle of filaments.

Yet another feature of the invention is the provision of such a yarnstructure wherein the plasticizing step comprises a step of drawing thebundle through a drawing die.

A still further feature of the invention is the provision of a method ofmaking a twisted yarn comprising the steps of providing a bundle ofparallel, spaced filaments with matrix material therebetween, effectinga plasticizing of the filaments in the bundle at a first limited portionof the length of the bundle, providing a twist in the plasticizedfilaments in the bundle by turning about its axis a second portion ofthe bundle, discontinuing the plasticizing of the filaments to cause thetwisted filaments to set in a substantially coaxial, spaced helicalconfiguration free of residual torsion, and removing the matrixmaterial.

Another feature of the invention is the provision of such a methodwherein the plasticizing step comprises a 'step of drawing of the bundlethrough a die, said first portion being disposed within the die and thesecond portion of the bundle being contiguous with the first portion.

A further feature of the invention is the provision of such a methodwherein the bundle is cold worked over 90%.

Still another feature of the invention is the provision of such a methodwherein the twist is provided in the bundle by application of twistingforces to the bundle portion entering the constricting means.

Yet another feature of the invention is the provision of such a methodwherein the twist is provided in the bundle by application of twistingforces to the bundle portion leaving the constricting means.

A further feature of the invention is the provision of a method ofmaking a twisted yarn comprising the steps of providing a bundle ofparallel filaments, effecting a plasticizing of the filaments in thebundle, twisting the plasticized filaments in the bundle, discontinuingthe plasticizing of the twisted filaments to cause the filaments to setin a helical configuration free of residual torsion, and removing thematrix material.

Other features and advantages of the invention will be apparent from thefollowing description taken in connection with the accompanying drawingswherein:

FIGURE 1 is a schematic layout of an exemplary apparatus for carryingout the method of forming yarn embodying the invention;

FIGURE 2 is a perspective view of a rod from which a yarn embodying theinvention may be formed;

FIGURE 2a is a cross sectional view of a rod enclosed in a sheath ofmatrix forming material;

FIGURE 3 is an enlarged diametric cross sectionof a die for use in themethod of the invention;

FIGURE 4 is a transverse cross section of a bundle of the sheathed rodsof FIG. 2a;

FIGURE 5 is a cross-section of the bundle of rods of FIG. 4 subsequentto a constriction thereof to form the rods therein into small diameterfilaments;

FIGURE 6 is a transverse cross section of the bundle of FIG. 5 having atwist imparted to the filaments therein by the method of the invention;

FIGURE 7 is a diagrammatic view illustrating the method embodying theinvention for providing the twisted bundle of FIG. 6;

FIGURE 8 is a diagrammatic view illustrating another method embodyingthe invention for providing the twisted bundles;

FIGURES 9-14 are diagrammatic views of additional different methodsembodying the invention for providing the twisted bundles;

FIGURE is a graph comparing the improved results of the invention withprior results;

FIGURE 16 is a graph comparing additional results of the invention withprior results;

FIGURE 17 is a fragmentary isometric view of a bundle of filamentswithout the matrix material;

FIGURE 18 is a transverse section taken substantially along the line18-18 of FIGURE 17;

FIGURE 19 is a transverse section similar to that of FIGURE 18, butwherein the filaments assume a position somewhat different from that ofFIGURE 18 but are still considered to be spaced;

FIGURE 20 is an elevational view of a short length of yarn twistedwithout a matrix material;

FIGURE 21 is a cross-sectional view of a bundle of filaments twisted ina die without matrix material;

FIGURE 22 is a chart illustrating the comparison between the mechanicalproperties of two bundles of yarn in a matrix subjected to a twist atdilferent times in the processing of the yarn;

FIGURE 23 is a graph illustrating the comparison between the mechanicalproperties of two bundles of yarn in matrices subjected to differentreductions in different dies; and

FIGURE 24 is a graph illustrating the comparison between mechanicalproperties of two bundles of yarn in matrices treated to a differentdegree of cold working.

In the exemplary embodiments of the invention as shown and described inthe drawing, similar reference numerals refer to similar partsthroughout the several views, an elongated element or filament 20 isprovided wi h a sheath or coating of a matrix 22 of a material differentfrom the material of the elongated element or filament 20. The elongatedelement or filament 20 is of a material capable of becoming somewhatfluid or plasticized under pressure such as the pressure created in aconstricting die.

The matrix material 22 can be initially bonded to the rod or filament 20in many ways such as by passing the composite through a constricting die24 or by applying the matrix onto the rod 20 in a fluid state wherebythe sheath will become bonded to the filament or rod 20 upon thesolidification of the matrix material 22 around the rod 20. Sometimesthe sheathed rod or filament 20 is passed through a few successivelysmaller dies to initially reduce the diameter of the rod or filament 20.

A plurality of like sheathed rods or filaments 20 are assembled togetherin a bundle of filaments 26 which bundle is then sheathed or embedded ina matrix 28 preferably of the same matrix material and the matrix boundbundle 26 of filaments 20 is fed consecutively through successivelysmaller constricting dies 24 to reduce the diameter of the bundle 26 andlikewise to reduce the diameter of the individual filaments 20 in thebundle. In some cases, just before the last draw of the bundle 26 offilaments 20 through the last constricting die 24, the bundle 26 offilaments 20 is wound onto a roll 30. The roll 30 is positioned on aspindle 32 carried by the frame 34 of the drawing machine 36 as shown inFIG- URE 1. A payout device 38 is shown as having an arm 40 pivoted at42 on the same axis as the drum or roll 30 and includes an eyelet 44through which the bundle 26 of filaments 20 is fed. The arm 40 is drivenabout the pivot axis in any will known manner so as to provide a twistto the bundle 26 and to guide the unwinding of the bundle 26 off theroll 30. The bundle 26 of filaments 20 is then passed through theconstricting or forming die 24, passed around a capstan 46, or othertensioning device and onto the rewinding roll 48.

As the capstan or tensioning device 46 pulls the bundle 26 of filaments20 through the die 24, the twist imparted to the filaments in the bundle26 is set into the bundle. That is, as the bundle 26 of filaments 20 andmatrix 22 is drawn through the die 24 the die working or constriction oneach progressive or successive increment of the bundle causes thematerial of the filaments 20 to become plasticized as the particularincrement is compressed under the relatively high hydrostatic pressuresof the die a 24. In some cases the matrix material will also becomefluid or plasticized. With the increment of the bundle of filaments in aplastic state, the twist imparted to the filaments by the payout device38 will be formed in the individual filaments 20 such that almostinstantaneously after the increment or segment of the bundle leaves thedie, the bundle of filaments takes a permanent set with the twist settherein. The filaments will be set free of residual torsion insubstantially coaxial spaced helical relationship. No further heattreatment is required on the bundle; however, subsequently processingcan be performed on the bundle if the ultimate use to be made of thebundle 26 of filaments so demands. The twist can be added to the bundleof filaments in successive steps a few twists at a time. Each time theconstricting die reduces the diameter of the bundle, producesinstantaneous plasticity and sets the twist imparted thereto by thetwisting device.

The twisted bundle of filaments with the matrix material therein is nextsubjected to either chemicals, heat or the like to remove the matrixmaterial to produce the bundle of twisted filaments or yarn ready foruse. A bundle of twisted filaments of the type just described issometimes called a yarn or a hollow yarn. With the matrix materialremoved from the bundle of filaments there will be an open space betweeneach filament and its adjacent filaments. FIGURES 17 and 18 illustratethe appearance and form of a bundle of filaments without the matrixmaterial. The filaments are referred to as being spaced from theiradjoining filaments. The term spaced is intended to include thecondition when the filaments in a bundle assume a position somewhatsimilar to the showing of FIGURE 19. That is, the filaments withoutmatrix could not just suspend themselves as shown in FIGURE 18 and willassume a position at rest wherein the filaments of each ring offilaments will settle or sag onto the inside of the immediatelycontiguous outside ring of filaments. Certain filaments will touchcertain other filaments at points along the length of the yarn, butessentially the filaments will be spaced apart. Therefore, when thefilaments are referred to as being spaced apart, it is intended that theincidental touching between filaments at spaced points throughout thecircumference, diameter and length of the yarn is to be included withinthe scope of the term.

There are certain parameters that influence the ultimate properties ofthe bundle or yarn 26 which has been twisted while it is passing througha constricting device, such as a die 24. Specifically, the die contouris important and in particular the percent or reduction of area of thebundle to be effected in the die, the die angle, the length of the diebearing surface and the relief angle of the die. The effect of thepercent reduction of area of the bundle due to the die will be discussedhereinafter with reference to FIGURE 21. If the die angle is too steepthe bundle will have a tendency to wedge or block up at the die openingwhich can cause rupturing of the bundle. If the die angle is tooshallow, the buildup of pressure will be over too great a distance andthe proper degree of plasticity for inducing the correct permanently settwist into the bundle or yarn 26 will not be reached. The relief radiusof the die should be standard as established in the trade. The dielubrication, the area of reduction of the cross section of the die andthe surface characteristics of the die and wire should be carefullycontrolled to produce the desired characteristics in the resulting yarn.A controlled back pull on the bundle of filaments entering the dieeffects better results in the yarn produced by the draw.

One embodiment of our invention known as Example I used a constrictingdevice, in this case a die having a polished tungsten carbide surface.The contour of the die included a die angle a of 12 (twelve degrees), abearing surface b of 4.4 mils which is 35% of the diameter of the bundlebeing drawn, and a standard relief radius c. The die was lubricated withApex 201 sulphated or chlorinated wire drawing oil. The die was designedto reduce the area of the bundle 20% during the twisting.

A bundle of 271 filaments of 0.5 mil diameter No. 304 stainless steelcold drawn wire was embedded in a matrix of Monel 400 material. The backpull on the bundle of filaments entering the die was approximately plusor minus 8 ounces. Applying seven (7) turns per inch to the bundle, asthe bundle was advanced into the die, each advancing increment of thebundle of filaments and matrix was heated due to the die working toabove the elastic limit of the material of the filaments whereupon eachincrement of the bundle of filaments became somewhat plastic such thatthe twist applied to the bundle permanently realigned the individualfilaments 20 in a new angular orientation with respect to the axis ofthe bundle. As each increment or discrete segment of the bundle 26emerged from the die 24, it immediately reset itself to the solid statewhereupon the bundle of filaments had a twist permanently set in thefilaments of the bundle. The bundle was then soaked in a chemical bathor heated to a preselected level to remove the Monel metal matrix,whereupon a hollow bundle of filaments having a tensile strength of295,000 pounds per square inch resulted. The resulting bundle offilaments or yarn is suitable for a wide variety of uses requiringeither strength or flexibility or combinations of both. The optimumtwist for the bundle of Example I was 9 turns per inch which produced ayarn having a breaking strength of 18.1 pounds.

FIGURE 7 is a diagrammatic or schematic showing of the same process asis illustrated in FIGURE 1, that is, in FIGURE 1 a twist is added to thebundle of filaments as the bundle is unwound from the roll 30. The twistof FIGURE 1 is illustrated in FIGURE 7 by a circular arrow 27 indicatinga twist in a clockwise direction to the bundle 26 as it is fed to thedie or constricting device 24.

FIGURE 8 shows a modified form oil the invention wherein the takeup roll50 and its mount 52 are rotated in a clockwise direction about the axis54 of the mount 52. In this way the twist is induced into the bundle offilaments as each increment or discrete segment of the bundle is in theplastic state in the die or constricting device 24. The twist is set inthe bundle of filaments immediately upon releasing the hydrostaticpressure on the increment of the bundle as each increment of the bundleemerges from the die. As the bundle is continuously advanced and thetwist is continuously applied, a bundle of filaments will be producedwith a continuous spiral or helix permanently set therein.

FEGURE 9 shows a modified form of the invention wherein the feed-in roll56 and takeup roll 58 are used only to unwind and wind the bundlethereon respectively. A loop 60 is formed in the bundle on thedownstream or exit side of the die 24. The loop 60 is then turned aboutthe axis of the bundle as shown by the arrow 62. The number of turns ofthe loop 60 about the axis of the bundle will determine the number oftwists induced in the bundle of filaments which is being drawn throughthe die 24. The twists or turns will be set in the bundle in theconstricting die as set out in detail above.

FIGURE 10 is similar to FIGURE 9 except that the loop 64 is on theentrance or upstream side of the die 24. There are times when the natureof the material making up the filaments 20 requires that the twist beadded to the bundle as the bundle enters the die instead of as thebundle leaves the die. The process is flexible enough to provide forboth. Different and improved results are obtained with differentfilament materials depending upon whether the twist is applied during orafter the bundle enters the die as will become apparent hereinafter.

FIGURE 11 shows a modified version of the invention wherein two dies orconstricting devices 24, 25 are spaced apart a short distance with aloop 64 in the bundle or composite therebetween. As the loop 64 isrotated about the axis of the bundle as the bundle is pulled through thesuccessive dies, the twist will be added progressively to the bundle,each die receiving and permitting permanently induced twist to thebundle as it passes therethrough.

FIGURES 12, 13 and 14 show another set of modifications for inducingtwist into a bundle of filaments. In FIGURE 12 a partial loop 66 iscreated in the bundle by training the bundle over or through a shapedpath. As the bundle is pulled through the die and around the shaped pathforming the loop 66 the loop 66 is rotated about the axis of the bundleto add a twist to the bundle as it is pulled through the die 24.

FIGURE 13 is similar to FIGURE 10 and shows a method of twisting thebundle by using the partial loop 66 in place of the Complete loop 64 asthe bundle is fed into the die. FIGURE 14 is similar to FIGURE 11wherein a partial loop 66 is used between successive constricting dies24, 25 for inducing twist into the bundle.

It has been found that although when an increment or discrete segment ofthe bundle of filaments is worked as it passes through the constrictingdie without twisting, the diameters of each filament in any crosssection taken across the width of the bundle will be substantially thesame. That is, in each size reduction of the whole bundle aproportionate size reduction will take place in each and every filamentsuch that the diameter of the center filament will be substantially thesame as the diameter of a filament in the outermost circle of filamentsin the bundle.

However, when a bundle such as shown in FIGURE 4 is twisted as it passescontinuously through the die 24, the cross section shown in FIGURE 5results, that is, the diameter of the filament at the center will bereduced at smaller amount as compared to the reduction in the diameterof the filament in the outer ring of filaments. There will be aproportional gradation in the diameters extending from the largest atthe center of the bundle and gradually reducing in diameter outward fromthe center until at the outermost ring of filaments the smallestdiameter of filaments will result. The degree or ratio of reduction willbe greater the greater the number of turns or twists per inch is putinto the bundle. It has been found that the addition of twists to thebundle will elongate the outermost filaments and reduce in diameter theoutermost filaments the most and will provide just enough elongationthat there will not be any lengthwise creep between concentric layers offilaments. For example, a one foot long straight bundle of filamentswill be some amount longer than one foot after the bundle is passedthrough the die with the twisting added, but the over-all axial lengthof the bundle will be the same even though the outermost filaments willnow be actually considerably longer due to the helix or spiral than thelength of the centermost filament. The twist can be added a few degreeseor a few turns per inch at a time by successive passes throughconstricting dies, each pass adding additional twist to the bundle.

The average area or sums of the cross section of all filaments isidentical no matter whether the bundle is passed through the diestraight or by adding a twist to the bundle as it passes through thedie. This is true even I though with a straight bundle all of thefilaments will have substantially identical cross sections resultingfrom the straight pass while with a twisted bundle the center filamentswill be larger in cross section and the filaments will graduallydecrease in diameter outward from the center. The radial distribution ofcross section obtained in the twisting process will produce a bundle offilaments or yarn having improved flex properties compared with atwisted bundle or yarn with no radial distribution of area of crosssection. Adding the twist while the bundle is in a state of plasticityin the die inherently produces a bundle of filaments of extremeuniformity of twist and extreme uniformity of weight per unit of length.

When tensile strength is an important factor, it has been found that amuch higher tensile strength can be obtained from a bundle of filamentstwisted in a matrix in a constricting device than can be obtained fromthe same bundle of filaments twisted after the matrix has been removedand without a constricting device. In particular, the tensile strengthof the bundle twisted in the matrix is increased as the number of turnsper inch is increased until a maximum or optimum tensile strength isobtained at a particular number of turns per inch. This, of course,varies with the types and diameters of the materials of the filaments.

FIGURE 15 illustrates in graphic form a set of comparison values for thematerial used in our Example I above, namely a 304 stainless filament.The horizontal calibration of the chart is in turns per inch and thevertical calibration is the yarn breaking load in pounds. The curvelabeled A is the yarn twisted without a matrix and without aconstricting die. It can be observed that the maximum or optimum valuesare reached at 2.5 turns per inch and 9.75 pounds breaking load. Curve Bis based on Example I above and is the same yarn as curve A embedded ina matrix of Monel 40-0 material and twisted in a constricting die. Thematrix is removed after the twist is set in the bundle. A maximumbreaking strength or load of 18.1 pounds was obtained at an optimum of 9turns or twists per inch. The values shown on the chart of FIG- URE 15clearly indicate the improved breaking strength that can be produced byproviding the twist to the bundle just prior to or as the bundle isbeing worked in the constricting die together with the improved resultsbased on the number of turns per inch in the bundle as compared to theprior system of twisting the bundle of filaments without a constrictingdie.

At the optimum twist in a bundle, which will be different for differentsizes and numbers of filaments, the tensile strength of the bundle willbe almost equal to of the individual or single filament strength. Thisis contrary to the usual results obtained when a bundle of filaments isreduced in diameter as by passing through a constricting die. Normallythere is a decrease in the tensile strength greater than theproportionate decrease in the diameters of each filament. Using ourinvention it has been found that at the optimum twist condition for aparticular bundle of filaments the tensile strength of the bundle willbe close to the full tensile strength of the combined individualfilament strengths.

When there is a dependence of the individual filament strength on thegauge length, the tensile strength of the bundle or yarn at optimumtwist corresponds to the zero gauge length tensile strength of theindividual filaments. In FIGURE 16 a comparison is made between singlefilament data, as shown by curve C, and a bundle or yarn data, as shownby curve D, at optimum twist condition. The vertical scale is thebreaking load in pounds while the horizontal scale is gauge length. Itis to be observed that as the gauge length of curve C increases, thebreaking load falls otf rather sharply. In the case of a bundle or yarnat optimum twist the breaking load remains constant for any reasonableincreases in the gauge length.

With the bundle of yarn capable of producing maximum tensile strengthsand nearly 100% translation of individual filament strengths, both atoptimum twist per unit of length, a superior bundle of filaments or yarnresults which is tougher and stronger and still has improved flexproperties. It is contemplated within the scope of the invention that atwisted filament yarn may be formed by passing a bundle of filamentswithout matrix material therebetween through the constricting devicewhile twist is added to the bundle. The resultant yarn has a permanentlyset twist free of torsion as in the above described embodiments but hasthe filaments set in engagement with each other. FIGURES 20 and 21 showa side and cross sectional view of a bundle of filaments with the twistset therein during the pass of the bundle through the die. The bundledoes not contain any matrix material and has the filaments set free oftorsion by the pass through the die as the twist is applied.

FIGURE 22 illustrates graphically the different results obtained inyarns that have been twisted in two different ways and either annealedor not annealed. In the first case, using the teaching of FIGURES 1 and7, the twist was applied to the bundle as the bundle entered the die andis shown in FIGURE 22 as curve III. Curve I is the bundle the same asFIGURES 1 and 7 only the bundle was annealed prior to twisting as itpassed into the die. In the second case, using the teaching of FIGURE 8,

the twist was applied downstream of the die or at the die exit as thebundle passed through the die and is shown in FIGURE 22 as the curve IV.Curve II is a bundle the same as FIGURE 8 only the bundle was annealedprior to passing through the die and with the twist applied at the exitor downstream of the die. FIG- URE 22 results from the following ExampleII:

Mechanical properties of heavily cold worked yarn twisted in a reductiondie Material 304 stainless steel Monel 400matrix.

Filament diameter 0.593 mil.

No. of filaments 301.

Reduction in die 20%.

/3 UTS Coeificient of variation of Twist and Percent L Cold Work Breako/X UIS, Breaka/X U'IS,

ing Load Percent ing Load percent 15 turns per inch 1 5.98 9. 7 5. S0 6.4

(95.1% cold worked) 9 turns per inch 5. 03 3. 2 5.11 3. 6

(97% cold Worked) 7 turns per inch. 4.79 5. 6 4.82 5.8

(97.5% cold worked) COMPOSITE OR BUNDLE TWISTEDANNEALED Entering the Die(II) Leaving the Die (1) Twist Breaking Load Breaking Load turns/inch9.1 l 11. 25 12 turns/inch" 10.9 25 turns/inch 3.8 9. 95

1 Optimum.

From these values and from the chart FIGURE 22, it can be seen that forthis type of material and matrix the addition of the twist to thecomposite or bundle from the downstream side of the die or on the exitend of the die produces varied results. Without annealing the additionof the twist to the bundle as it enters the die produces better resultsthan adding the twist on the exit side of the die. However, when thebundle is annealed before twisting in the die, the results arephenomenally better no matter whether the twist is added on the entranceor on the exit end of the die. The annealed bundle u when twisted fromthe exit end of the die produces the strongest torsion free yarn as isshown by curve I in FIGURE 22. The bundle that was annealed and twistedas it entered the die produced very strong yarns also as shown by curveII in FIGURE 22.

Example III illustrates the efiect of the magnitude of reduction of thearea of the bundle in the twisting die on the optimum turns per inch andbreaking load of the bundle. FIGURE 23 illustrates the graphic resultsof twisting several bundles of filaments having the followingcharacteristics:

Material 304 stainless steel. Matrix 400 Monel metal. Total cold work93.8%.

No. of filaments 271.

Filament diameter 0.593 mil.

Curve I is the result of values received from bundles twisted in a dieproducing 36% reduction in the area of the bundle as the bundle passedthrough the die. Curve II is the result of values received from bundlestwisted in a die producing reduction in the area of the bundle as thebundle passed through the die. It will be noted that the total breakingload in both cases reaches about the same maximum of about 23 pounds.The difference is in the fact that the bundles receiving the greaterpercent reduction in area during the twisting reached the optimumbreaking load with 5 turns per inch where the bundles receiving thelesser reduction in area produced their maximum breaking load at 8 turnsper inch.

Example IV illustrates the effect of yarn diameter on twistingcharacteristics together with the effect of filament diameters on theultimate tensile strength. FIGURE 24 illustrates the results of twistingseveral bundles of filaments having the following characteristics:

Material 304 stainless steel. Matrix 400 Monel metal. Reduction in die20%.

No. of filaments 301.

Curve I is the result of applying the twist to filaments having adiameter of 1.005 mil, while curve II is the result of applying thetwist to filaments having a diameter of 0.580 mil. It will be noted thatan optimum ultimate tensile strength of 365,000 pounds per square inchwas reached at around 4.5 turns per inch using the 1.005 mil filament(curve I) while the optimum ultimate tensile strength of 276,000 poundsper square inch was reached at about 8 turns per inch using the 0.580mil filament (curve II).

The twisted torsion free bundle or yarn may have many unique geometricalconfigurations which will impart particularly desirable properties tothe yarn for specific applications. With the matrix material removed, atwisted bundle of filaments or yarn has the individual filaments in atorsion free, uniaxial helical configuration such that the bundle oryarn will have the property of high elongation. That is, as the yarn ispulled lengthwise the outer filaments will close in on the innerfilaments permitting the yarn to appear to stretch lengthwise which isdesirable for certain applications for which the yarn can be used.

The twisted yarn can have the individual filaments with high surfaceroughness or wherein the surface chemical composition can be differentas a result of interdiffusion of the matrix with the filament materialduring the repeated plasticized states caused by the successive passesthrough the constricting die. The surface condition, i.e., roughness ormodified chemical composition, together with the twist to the filaments,can radically influence the transference or equalization of stress onthe filaments of the bundle and thus produce the high translation ofsingle filament to yarn strength.

Using the teaching of this invention, it is possible to induce thetorsion free twist into the material of the filaments in a heavily coldworked condition. No external heat need be added to the die area toeither create the plastic state of the material of the filaments or tostress relieve the twisted bundles after the twist has been inducedtherein in the die.

The method of producing the hydrostatic pressure on the filament orbundle of filaments is by means of a constricting device. Theconstricting device referred to here inbefore is generally aconstricting die. However, there are other mechanical constrictingdevices which can be used such as roller dies and rolls which can beused on materials in either a hot or cold condition. It is also possibleto use a high pressure fluid to maintain die pressure sufficiently highto create a state of plasticity under the hydrostatic pressuresufficient to induce and set a torsion free twist in a bundle offilaments to produce a torsion free yarn of desirable characteristicsnot heretofore contemplated.

While we have shown and described certain embodiments of our invention,his to be understood that it is capable of many modifications. Changes,therefore, in the construction and arrangement may be made withoutdeparting from the spirit and scope of the invention as defined in theappended claims.

We claim:

1. A yarn structure comprising a plurality of cold worked, unannealedmetallic filaments twisted while under pressure in a substantiallynonelastic state and set free of residual torsion in substantiallycoaxial, spaced helical relationship and movably associated to haveengagement therebetween.

2. The yarn structure of claim. 1 wherein said metallic filaments areformed of stainless steel.

3. The yarn structure of claim 1 wherein the number of turns per inch ofthe helical filaments is preselected to provide a yarn strengthsubstantially equal to the zero gauge length strength of said filaments.

4. The yarn structure of claim 1 wherein the total area of saidfilaments transverse to the axis of the yarn is substantially constantalong said axis.

5. The yarn structure of claim 1 wherein said filaments are disposed inradially spaced, generally cylindrical groups.

6. The yarn structure of claim 1 wherein said plurality of filamentsfurther includes an axial, substantially rectilinear filament having adiameter larger than the helical filaments.

7. The yarn structure of claim 1 wherein said plurality of filamentsincludes filaments spaced at different distances radially of the axis ofthe set plurality, the diam- References Cited UNITED STATES PATENTS1,012,031 12/1911 Underwood 139-425 1,096,077 5/1914 Underwood.2,050,298 8/ 1936 Everett 29423 X 2,077,682. 4/1937 Everett 294192,532,395 12/1950 Dreyfus 57-140 3,077,72 r 2/1963 Stoddard et a1. 57-343,090,189 5/1963 Boussu et al. 57139 3,090,190 5/1963 Boussu et al57-139 3,277,564 10/1966 Webber et al 29419 3,288,175 11/1966 Valko57l39 X FOREIGN PATENTS 966,846 8/ 1964 Great Britain.

JOHN PETRAKES, Primary Examiner.

